backup

CD-R

Multisession CD onto which users can record their own items, such as text, graphics, and audio. Each part of a CD-R can be written on only one time, though one part of the disc can be written at one time and another part at a later time. Once recorded, a CD-R can be read from as many times as necessary, but its contents cannot be erased. CD-R is short for compact disc-recordable

CD-R drive

CD-ROM

Type of optical disc that uses laser technology to store data, instructions, and information. A CD-ROM can contain text, graphics, video, and audio. Manufacturers write, or record, the contents of standard CD-ROMs in a single session, and users only can read the contents, not erase or modify them. A typical CD-ROM can hold from 650 MB to 1 GB of data. CD-ROM is short for compact disc read-only memory

DVD+RAM

DVD+RW

DVD-ROM

Type of optical disc that can be erased and written to, or recorded on, more than 1,000 times. A DVD+RW is similar to a CD-RW, except it has storage capacities up to 3 GB per side. DVD+RW is short for DVD-rewriteable

formatting

hard disk

Type of storage device that contains one or more inflexible, circular platters that store data, instructions, and information. A hard disk stores data magnetically and is a read/write storage medium, meaning it can be read from and written to any number of times. Also called hard disk drive

tape

allocation unit

The smallest unit of disk space that stores data, consisting of two to eight sectors on a single track on a hard disk. A single allocation unit, which also is called a cluster or a block, holds data from only one file

BD-RE

Blu-ray Disk-rom

burning

cluster

The smallest unit of disk space that stores data, consisting of two to eight sectors on a single track on a hard disk. A single cluster, which also is called an allocation unit or a block, holds data from only one file

cylinder

density

direct access

Type of data access in which the storage device is able to locate a particular data item or file immediately, without having to move consecutively through items stored in front of the desired data item or file. Also called random access

disk cache

disk controller

Special-purpose chip and electronic circuits that control the transfer of data, instructions, and information between a disk and the system bus and other components in a computer. Sometimes called an interface

EIDE

Interface used in controllers that can support up to four hard disks at 137 GB per disk, transfer data at speeds up to 66 MBps, and provide connections for CD, DVD, and tape drives. EIDE controllers are one of the more widely used controllers for hard disks

perpendicular recording

random access

Type of data access in which the storage device is able to locate a particular data item or file immediately, without having to move consecutively through items stored in front of the desired data item or file. Also called direct access

SATA

sectors

sequential access

Type of data access in which the storage device reads or writes data consecutively. In order to locate a particular data item or file, the device has to move consecutively through items stored in front of the desired data item or file before reaching the file

single-session disk

Disc that is written to only once and cannot be written to again. Manufacturers typically produce a single-session disc by writing all items on the disc at one time, before distributing the disc to users